Architecture For Variable Motion Control Envelope

ABSTRACT

The technology employs a variable motion control envelope that enables an on-board computing system of a self-driving vehicle to estimate future vehicle driving behavior along an upcoming path, in order to maintain a desired amount of control during autonomous driving. Factors including intrinsic vehicle properties, extrinsic environmental influences and road friction information are evaluated. Such factors can be evaluated to derive an available acceleration model, which defines an envelope of maximum longitudinal and lateral accelerations for the vehicle. This model, which may identify dynamically varying acceleration limits that can be affected by road conditions and road configurations, may be used by the on-board control system (e.g., a planner module of the processing system) to control driving operations of the vehicle in an autonomous driving mode.

BACKGROUND

Self-driving vehicles that operate in an autonomous driving mode maytransport passengers, cargo or other items from one location to another.Vehicle handling is constrained, in part, by the friction interaction oftires and the road surface, the available actuation forces produced bythe vehicle, and forces due to external factors such as road grade,bank, wind gusts, etc. Such constraint factors can significantly affectongoing driving operations and path planning for upcoming portions of atrip.

BRIEF SUMMARY

The technology relates to employing a variable motion control envelopethat allows the on-board computing system of a self-driving vehicle toestimate future vehicle behavior along an upcoming path, in order tomaintain desired control during autonomous driving. Various factors suchas intrinsic vehicle properties and extrinsic environmental influencesare evaluated. Different factors may be readily quantifiable (e.g.,vehicle center of gravity), may change in a discrete or deterministicmanner (e.g., a steering electronic control unit failure), or may behighly variable in the spatial and/or temporal domains (e.g., changes inroad surface friction due to precipitation, oil or other substances).Such factors may be evaluated to derive an available acceleration model,which defines an envelope of maximum longitudinal and lateralaccelerations for the vehicle. This model, which may identifydynamically varying acceleration limits that can be affected by roadconditions and road configurations, may be used by the on-board controlsystem (e.g., a planner module of the processing system) to controldriving operations of the vehicle in an autonomous driving mode.

According to one aspect, a method of operating a vehicle in anautonomous driving mode is provided. The method comprises estimating, byone or more processors of the vehicle, a local friction envelope basedon at least one of road surface information and tire state data from oneor more tires of the vehicle; estimating, by the one or more processors,an external force impact on the vehicle based on at least one of a localgravity vector and environmental forces; estimating, by the one or moreprocessors, an internal force impact on the vehicle based on at leastone of steering, braking, propulsion or vehicle kinetic information ofthe vehicle; generating, by the one or more processors, an availableacceleration model for the vehicle based on the estimated local frictionenvelope, the estimated external force impact and the estimated internalforce impact; producing, by the one or more processors, a tractiongeneration profile based on the available acceleration model; andcontrolling the vehicle, by the one or more processors in the autonomousdriving mode, according to the traction generation profile.

In one example, controlling the vehicle includes at least one ofchanging a driving action or updating an operating plan for an upcomingsection of roadway. In another example, the traction generation profilecomprises a variable motion control envelope that is updatedperiodically during operation in the autonomous driving mode. In afurther example, the traction generation profile comprises a variablemotion control envelope that is updated between iterations of a pathgenerated by the one or more processors. In yet another example, thetraction generation profile comprises a variable motion control envelopethat is updated upon occurrence of an action, event or conditionimpacting the motion control envelope.

The method may further include updating the traction generation profilespatially according to different segments of a roadway.

Estimating the local friction envelope may be based on the tire statedata, longitudinal and lateral slip information, and an adaptive valuefor a friction coefficient of the road surface information. The localgravity vector may be a measure of a local bank and a grade of a roadwaysegment. The environmental forces may include wind disturbanceinformation.

According to another aspect, a vehicle is configured to operate in anautonomous driving mode. The vehicle comprises a perception systemincluding one or more sensors configured to receive sensor dataassociated with an external environment of the vehicle including aportion of a roadway; a driving system including a steering subsystem,an acceleration subsystem and a deceleration subsystem to controldriving of the vehicle; a positioning system configured to determine acurrent position of the vehicle; and a control system including one ormore processors. The control system is operatively coupled to thedriving system, the perception system and the positioning system. Thecontrol system is configured to estimate a local friction envelope basedon at least one of road surface information and tire state data from oneor more tires of the vehicle; estimate an external force impact on thevehicle based on at least one of a local gravity vector along theportion of the roadway and environmental forces in the externalenvironment; estimate an internal force impact on the vehicle based onat least one of steering, braking, propulsion or vehicle kineticinformation of the vehicle; generate an available acceleration model forthe vehicle based on the estimated local friction envelope, theestimated external force impact and the estimated internal force impact;produce a traction generation profile based on the availableacceleration model; and control the vehicle in the autonomous drivingmode according to the traction generation profile.

According to a further aspect, a method of operating a vehicle in anautonomous driving mode includes generating, by one or more processorsof the vehicle, an initial friction estimation based on a road surfaceclassification for a portion of a roadway and weather data for anexternal environment of the vehicle; generating, by the one or moreprocessors, an on-line friction estimate based on the initial frictionestimation, pose information of the vehicle on the portion of theroadway, and wheel speed information of the vehicle; generating, by theone or more processors, a set of acceleration limits based on theon-line friction estimate and the pose information; and controlling thevehicle along the roadway, by the one or more processors in theautonomous driving mode, according to the set of acceleration limits.

Generating the initial friction estimate may include adjusting frictionbounds according to a wetness along the portion of the roadway.Generating the initial friction estimate may alternatively oradditionally include weighting the road surface classification moreheavily than the weather data.

The on-line friction estimate may be further based on additionalinformation associated with how much torque is applied to one or moretires of the vehicle. Here, the additional information may include atleast one of actuation forces or a tire normal force estimation. Theon-line friction estimate may be adaptive in real-time during drivingalong the portion of the roadway in accordance with the pose informationand wheel speed information.

Generating the set of acceleration limits may include generating a setof corrective control inputs and recovery state information. Here, therecovery state information may provide a target trajectory forstabilizing the vehicle.

The set of acceleration limits may be associated with a set ofcorrective control inputs and a set of primary control inputs. In thiscase, the set of corrective control inputs is obtained from the on-linefriction estimate and the pose information, and the set of primarycontrol inputs is obtained from the on-line friction estimate andtrajectory information of the vehicle. Here, controlling the vehicle maybe performed based on a combination of the corrective control inputs andthe primary control inputs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B illustrate example self-driving vehicles in accordance withaspects of the technology.

FIGS. 1C-D illustrate an example cargo-type vehicle configured for usewith aspects of the technology.

FIG. 2 illustrates components of a self-driving vehicle in accordancewith aspects of the technology.

FIGS. 3A-B are block diagrams of systems of an example cargo-typevehicle in accordance with aspects of the technology.

FIG. 4 illustrates an example envelope of feasible accelerations inaccordance with aspects of the technology.

FIG. 5 illustrates an example envelope of maximum acceleration inaccordance with aspects of the technology.

FIG. 6 illustrates an example functional architecture in accordance withaspects of the technology.

FIGS. 7A-B illustrates an example implementation architecture inaccordance with aspects of the technology.

FIGS. 8A-B illustrate an example system in accordance with aspects ofthe technology.

FIG. 9 illustrates an example method in accordance with aspects of thetechnology.

FIG. 10 illustrates another example method in accordance with aspects ofthe technology.

DETAILED DESCRIPTION

A functional architecture is provided for a self-driving vehicle thatcan manage a variable motion control envelope that is impacted byvarious factors, including rapidly changing environmental conditions,tire wear and actuator states. Intrinsic and extrinsic forces areevaluated, including looking at both the ranges of accelerations thevehicle can produce and the range of external disturbance accelerations,for instance to determine whether the sum of such accelerations would beless than a limiting acceleration due to friction of the tires on theroad surface. Feasible and stable planning can be achieved in variousvehicle/environmental states when the computer system (e.g., a plannermodule of the on-board processing system) uses an available acceleration(and accelerate rate) model to create driving plans that take intoaccount modified lateral and longitudinal acceleration limits which aredynamic in time and space.

Example Vehicle Systems

FIG. 1A illustrates a perspective view of an example passenger vehicle100, such as a minivan or sport utility vehicle (SUV), configured tooperate in a self-driving mode. FIG. 1B illustrates a perspective viewof another example passenger vehicle 150 that is configured to operatein a self-driving mode, such as a sedan. These passenger vehicles mayinclude various sensors for obtaining information about the vehicle'sexternal environment. For instance, a roof-top housing unit (roof podassembly) 102 may include a lidar sensor as well as various cameras(e.g., optical or infrared), radar units, acoustical sensors (e.g.,microphone or sonar-type sensors), inertial (e.g., accelerometer,gyroscope, etc.) or other sensors (e.g., positioning sensors such as GPSsensors). Housing 104, located at the front end of vehicle 100, andhousings 106 a, 106 b on the driver's and passenger's sides of thevehicle may each incorporate lidar, radar, camera and/or other sensors.For example, housing 106 a may be located in front of the driver's sidedoor along a quarter panel of the vehicle. As shown, the passengervehicle 100 also includes housings 108 a, 108 b for radar units, lidarand/or cameras also located towards the rear roof portion of thevehicle. Additional lidar, radar units and/or cameras (not shown) may belocated at other places along the vehicle 100. For instance, arrow 110indicates that a sensor unit (not shown) may be positioned along therear of the vehicle 100, such as on or adjacent to the bumper. Dependingon the vehicle type and sensor housing configuration(s), acousticalsensors may be disposed in any or all of these housings around thevehicle.

Arrow 114 indicates that the roof pod 102 as shown includes a basesection coupled to the roof of the vehicle. And arrow 116 indicated thatthe roof pod 102 also includes an upper section raised above the basesection. Each of the base section and upper section may house differentsensor units configured to obtain information about objects andconditions in the environment around the vehicle. The roof pod 102 andother sensor housings may also be disposed along vehicle 150 of FIG. 1B.By way of example, each sensor unit may include one or more sensors ofthe types described above, such as lidar, radar, camera (e.g., opticalor infrared), acoustical (e.g., a passive microphone or active soundemitting sonar-type sensor), inertial (e.g., accelerometer, gyroscope,etc.) or other sensors (e.g., positioning sensors such as GPS sensors).

FIGS. 1C-D illustrate an example cargo vehicle 150, such as atractor-trailer truck, that is configured to operate in a self-drivingmode. The truck may include, e.g., a single, double or triple trailer,or may be another medium or heavy duty truck such as in commercialweight classes 4 through 8. As shown, the truck includes a tractor unit152 and a single cargo unit or trailer 154. The trailer 154 may be fullyenclosed, open such as a flat bed, or partially open depending on thetype of cargo to be transported. In this example, the tractor unit 152includes the engine and steering systems (not shown) and a cab 156 for adriver and any passengers.

The trailer 154 includes a hitching point, known as a kingpin, 158. Thekingpin 158 is typically formed as a solid steel shaft, which isconfigured to pivotally attach to the tractor unit 152. In particular,the kingpin 158 attaches to a trailer coupling 160, known as afifth-wheel, that is mounted rearward of the cab. For a double or tripletractor-trailer, the second and/or third trailers may have simple hitchconnections to the leading trailer. Or, alternatively, each trailer mayhave its own kingpin. In this case, at least the first and secondtrailers could include a fifth-wheel type structure arranged to coupleto the next trailer.

As shown, the tractor may have one or more sensor units 162, 164disposed therealong. For instance, one or more sensor units 162 may bedisposed on a roof or top portion of the cab 156, and one or more sidesensor units 164 may be disposed on left and/or right sides of the cab156. Sensor units may also be located along other regions of the cab156, such as along the front bumper or hood area, in the rear of thecab, adjacent to the fifth-wheel, underneath the chassis, etc. Thetrailer 154 may also have one or more sensor units 166 disposedtherealong, for instance along a side panel, front, rear, roof and/orundercarriage of the trailer 154.

As with the sensor units of the passenger vehicles of FIGS. 1A-B, eachsensor unit of the cargo vehicle may include one or more sensors, suchas lidar, radar, camera (e.g., optical or infrared), acoustical (e.g.,microphone or sonar-type sensor), inertial (e.g., accelerometer,gyroscope, etc.) or other sensors (e.g., positioning sensors such as GPSsensors).

While certain aspects of the disclosure may be particularly useful inconnection with specific types of vehicles, the vehicle may be differenttypes of vehicle including, but not limited to, cars, motorcycles, cargovehicles, buses, recreational vehicles, emergency vehicles, constructionequipment, etc.

There are different degrees of autonomy that may occur for a vehicleoperating in a partially or fully autonomous driving mode. The U.S.National Highway Traffic Safety Administration and the Society ofAutomotive Engineers have identified different levels to indicate howmuch, or how little, the vehicle controls the driving. For instance,Level 0 has no automation and the driver makes all driving-relateddecisions. The lowest semi-autonomous mode, Level 1, includes some driveassistance such as cruise control. At this level, the vehicle mayoperate in a strictly driver-information system without needing anyautomated control over the vehicle. Here, the vehicle's onboard sensors,relative positional knowledge between them, and a way for them toexchange data, can be employed to implement aspects of the technology asdiscussed herein. Level 2 has partial automation of certain drivingoperations, while Level 3 involves conditional automation that canenable a person in the driver's seat to take control as warranted. Incontrast, Level 4 is a high automation level where the vehicle is ableto drive without assistance in select conditions. And Level 5 is a fullyautonomous mode in which the vehicle is able to drive without assistancein all situations. The architectures, components, systems and methodsdescribed herein can function in any of the semi or fully-autonomousmodes, e.g., Levels 1-5, which are referred to herein as autonomousdriving modes. Thus, reference to an autonomous driving mode includesboth partial and full autonomy.

FIG. 2 illustrates a block diagram 200 with various components andsystems of an exemplary vehicle, such as passenger vehicle 100 or 150,to operate in an autonomous driving mode. As shown, the block diagram200 includes one or more computing devices 202, such as computingdevices containing one or more processors 204, memory 206 and othercomponents typically present in general purpose computing devices. Thememory 206 stores information accessible by the one or more processors204, including instructions 208 and data 210 that may be executed orotherwise used by the processor(s) 204. The computing system may controloverall operation of the vehicle when operating in an autonomous drivingmode.

The memory 206 stores information accessible by the processors 204,including instructions 208 and data 210 that may be executed orotherwise used by the processors 204. For instance, the memory mayinclude illumination-related information to perform, e.g., occludedvehicle detection. The memory 206 may be of any type capable of storinginformation accessible by the processor, including a computingdevice-readable medium. The memory is a non-transitory medium such as ahard-drive, memory card, optical disk, solid-state, etc. Systems mayinclude different combinations of the foregoing, whereby differentportions of the instructions and data are stored on different types ofmedia.

The instructions 208 may be any set of instructions to be executeddirectly (such as machine code) or indirectly (such as scripts) by theprocessor(s). For example, the instructions may be stored as computingdevice code on the computing device-readable medium. In that regard, theterms “instructions”, “modules” and “programs” may be usedinterchangeably herein. The instructions may be stored in object codeformat for direct processing by the processor, or in any other computingdevice language including scripts or collections of independent sourcecode modules that are interpreted on demand or compiled in advance. Thedata 210 may be retrieved, stored or modified by one or more processors204 in accordance with the instructions 208. In one example, some or allof the memory 206 may be an event data recorder or other secure datastorage system configured to store vehicle diagnostics and/or detectedsensor data, which may be on board the vehicle or remote, depending onthe implementation.

The processors 204 may be any conventional processors, such ascommercially available CPUs. Alternatively, each processor may be adedicated device such as an ASIC or other hardware-based processor.Although FIG. 2 functionally illustrates the processors, memory, andother elements of computing devices 202 as being within the same block,such devices may actually include multiple processors, computingdevices, or memories that may or may not be stored within the samephysical housing. Similarly, the memory 206 may be a hard drive or otherstorage media located in a housing different from that of theprocessor(s) 204. Accordingly, references to a processor or computingdevice will be understood to include references to a collection ofprocessors or computing devices or memories that may or may not operatein parallel.

In one example, the computing devices 202 may form an autonomous drivingcomputing system incorporated into vehicle 100. The autonomous drivingcomputing system may be capable of communicating with various componentsof the vehicle. For example, the computing devices 202 may be incommunication with various systems of the vehicle, including a drivingsystem including a deceleration system 212 (for controlling braking ofthe vehicle), acceleration system 214 (for controlling acceleration ofthe vehicle), steering system 216 (for controlling the orientation ofthe wheels and direction of the vehicle), signaling system 218 (forcontrolling turn signals), navigation system 220 (for navigating thevehicle to a location or around objects) and a positioning system 222(for determining the position of the vehicle, which may include thevehicle's pose, e.g., position and orientation along the roadway orpitch, yaw and roll of the vehicle chassis relative to a coordinatesystem). The autonomous driving computing system may employ a plannermodule 223, in accordance with the navigation system 220, thepositioning system 222 and/or other components of the system, e.g., fordetermining a route from a starting point to a destination or for makingmodifications to various driving aspects in view of current or expectedtraction conditions.

The computing devices 202 are also operatively coupled to a perceptionsystem 224 (for detecting objects in the vehicle's environment), a powersystem 226 (for example, a battery and/or gas- or diesel-powered engine)and a transmission system 230 in order to control the movement, speed,etc., of the vehicle in accordance with the instructions 208 of memory206 in an autonomous driving mode which does not require or needcontinuous or periodic input from a passenger of the vehicle. Some orall of the wheels/tires 228 are coupled to the transmission system 230,and the computing devices 202 may be able to receive information abouttire pressure, balance and other factors that may impact driving in anautonomous mode.

The computing devices 202 may control the direction and speed of thevehicle, e.g., via the planner module 223, by controlling variouscomponents. By way of example, computing devices 202 may navigate thevehicle to a particular location, such as a destination or intermediatestop or waypoint along a route, completely autonomously using data fromthe map information and navigation system 220. Computing devices 202 mayuse the positioning system 222 to determine the vehicle's location andthe perception system 224 to detect and respond to objects when neededto reach the location safely. In order to do so, computing devices 202may cause the vehicle to accelerate (e.g., by increasing fuel or otherenergy provided to the engine by acceleration system 214), decelerate(e.g., by decreasing the fuel supplied to the engine, changing gears,and/or by applying brakes by deceleration system 212), change direction(e.g., by turning the front and/or other wheels of vehicle 100 bysteering system 216), and signal such changes (e.g., by lighting turnsignals of signaling system 218). Thus, the acceleration system 214 anddeceleration system 212 may be a part of a drivetrain or other type oftransmission system 230 that includes various components between anengine of the vehicle and the wheels of the vehicle. Again, bycontrolling these systems, computing devices 202 may also control thetransmission system 230 of the vehicle in order to maneuver the vehicleautonomously.

Navigation system 220 may be used by computing devices 202 in order todetermine and follow a route to a location. In this regard, thenavigation system 220 and/or memory 206 may store map information, e.g.,highly detailed maps that computing devices 202 can use to navigate orcontrol the vehicle. As an example, these maps may identify the shapeand elevation of roadways (e.g., including road inclination/declination,banking or other curvature, etc.), lane markers, intersections,crosswalks, speed limits, traffic signal lights, buildings, signs, realtime traffic information, vegetation, or other such objects andinformation. The lane markers may include features such as solid orbroken double or single lane lines, solid or broken lane lines,reflectors, etc. A given lane may be associated with left and/or rightlane lines or other lane markers that define the boundary of the lane.Thus, most lanes may be bounded by a left edge of one lane line and aright edge of another lane line.

The perception system 224 includes sensors 232 for detecting objectsexternal to the vehicle. The detected objects may be other vehicles,obstacles in the roadway, traffic signals, signs, trees, etc. Thesensors may 232 may also detect certain aspects of weather conditions,such as snow, rain or water spray, or puddles, ice or other materials onthe roadway.

By way of example only, the sensors of the perception system may includelight detection and ranging (lidar) sensors, radar units, cameras (e.g.,optical imaging devices, with or without a neutral-density filter (ND)filter), positioning sensors (e.g., gyroscopes, accelerometers and/orother inertial components), infrared sensors, and/or any other detectiondevices that record data which may be processed by computing devices202. The perception system 224 may also include one or more microphonesor other acoustical arrays, for instance arranged along the roof pod 102and/or other sensor assembly housings. The microphones may be capable ofdetecting sounds across a wide frequency band (e.g., 50 Hz-25 KHz) suchas to detect various types of noises such as horn honks, tire squeals,brake actuation, etc.

Such sensors of the perception system 224 may detect objects outside ofthe vehicle and their characteristics such as location, orientation(pose) relative to the roadway, size, shape, type (for instance,vehicle, pedestrian, bicyclist, etc.), heading, speed of movementrelative to the vehicle, etc., as well as environmental conditionsaround the vehicle. The perception system 224 may also include othersensors within the vehicle to detect objects and conditions within thevehicle, such as in the passenger compartment. For instance, suchsensors may detect, e.g., one or more persons, pets, packages, etc., aswell as conditions within and/or outside the vehicle such astemperature, humidity, etc. Information regarding the positioning ofpassengers, packages or other objects within the vehicle may helpdetermine a center of gravity of the vehicle during a trip. Stillfurther sensors 232 of the perception system 224 may measure the rate ofrotation and/or pointing angle of the wheels 228, an amount or a type ofbraking by the deceleration system 212, and other factors associatedwith the equipment of the vehicle itself.

The raw data obtained by the sensors can be processed by the perceptionsystem 224 and/or sent for further processing to the computing devices202 periodically or continuously as the data is generated by theperception system 224. Computing devices 202 may use the positioningsystem 222 to determine the vehicle's location and perception system 224to detect and respond to objects when needed to reach the locationsafely, e.g., via adjustments made by planner module 223, includingadjustments in operation to deal with occlusions, slippery road surfacesand other issues. In addition, the computing devices 202 may performvalidation or calibration of individual sensors, all sensors in aparticular sensor assembly, or between sensors in different sensorassemblies or other physical housings.

As illustrated in FIGS. 1A-B, certain sensors of the perception system224 may be incorporated into one or more sensor assemblies or housings.In one example, these may be integrated into front, rear or sideperimeter sensor assemblies around the vehicle. In another example,other sensors may be part of the roof-top housing (roof pod) 102. Thecomputing devices 202 may communicate with the sensor assemblies locatedon or otherwise distributed along the vehicle. Each assembly may haveone or more types of sensors such as those described above.

Returning to FIG. 2, computing devices 202 may include all of thecomponents normally used in connection with a computing device such asthe processor and memory described above as well as a user interfacesubsystem 234. The user interface subsystem 234 may include one or moreuser inputs 236 (e.g., a mouse, keyboard, touch screen and/ormicrophone) and one or more display devices 238 (e.g., a monitor havinga screen or any other electrical device that is operable to displayinformation). In this regard, an internal electronic display may belocated within a cabin of the vehicle (not shown) and may be used bycomputing devices 202 to provide information to passengers within thevehicle. Other output devices, such as speaker(s) 240 may also belocated within the passenger vehicle.

The vehicle may also include a communication system 242. For instance,the communication system 242 may also include one or more wirelessconfigurations to facilitate communication with other computing devices,such as passenger computing devices within the vehicle, computingdevices external to the vehicle such as in other nearby vehicles on theroadway, and/or a remote server system. The network connections mayinclude short range communication protocols such as Bluetooth™,Bluetooth™ low energy (LE), cellular connections, as well as variousconfigurations and protocols including the Internet, World Wide Web,intranets, virtual private networks, wide area networks, local networks,private networks using communication protocols proprietary to one ormore companies, Ethernet, WiFi and HTTP, and various combinations of theforegoing.

FIG. 3A illustrates a block diagram 300 with various components andsystems of a vehicle configured for autonomous driving, e.g., vehicle150 of FIGS. 1C-D. By way of example, the vehicle may be a truck, farmequipment or construction equipment, configured to operate in one ormore autonomous modes of operation. As shown in the block diagram 300,the vehicle includes a control system of one or more computing devices,such as computing devices 302 containing one or more processors 304,memory 306 and other components similar or equivalent to components 202,204 and 206 discussed above with regard to FIG. 2.

The control system may constitute an electronic control unit (ECU) of atractor unit of a cargo vehicle. As with instructions 208, theinstructions 308 may be any set of instructions to be executed directly(such as machine code) or indirectly (such as scripts) by the processor.Similarly, the data 310 may be retrieved, stored or modified by one ormore processors 304 in accordance with the instructions 308.

In one example, the computing devices 302 may form an autonomous drivingcomputing system incorporated into vehicle 150. Similar to thearrangement discussed above regarding FIG. 2, the autonomous drivingcomputing system of block diagram 300 may be capable of communicatingwith various components of the vehicle in order to perform routeplanning and driving operations. For example, the computing devices 302may be in communication with various systems of the vehicle, such as adriving system including a deceleration system 312, acceleration system314, steering system 316, signaling system 318, navigation system 320and a positioning system 322, each of which may function as discussedabove regarding FIG. 2.

The computing devices 302 are also operatively coupled to a perceptionsystem 324, a power system 326 and a transmission system 330. Some orall of the wheels/tires 228 are coupled to the transmission system 230,and the computing devices 202 may be able to receive information abouttire pressure, balance, rotation rate, wheel angle, wear, and otherfactors that may impact driving in an autonomous mode. As with computingdevices 202, the computing devices 302 may control the direction andspeed of the vehicle by controlling various components. By way ofexample, computing devices 302 may navigate the vehicle to a destinationlocation completely autonomously using data from the map information andnavigation system 320. Computing devices 302 may employ a planner module323, in conjunction with the positioning system 322, the perceptionsystem 324 and other subsystems to detect and respond to objects whenneeded to reach the location safely, similar to the manner describedabove for planner module 223 FIG. 2.

Similar to perception system 224, the perception system 324 alsoincludes one or more sensors or other components such as those describedabove for detecting objects external to the vehicle, objects orconditions internal to the vehicle, and/or operation of certain vehicleequipment such as the wheels 328, deceleration system 312, accelerationsystem 314, steering system 316, transmission system 330, etc. Forinstance, as indicated in FIG. 3A the perception system 324 includes oneor more sensor assemblies 332. Each sensor assembly 232 includes one ormore sensors. In one example, the sensor assemblies 332 may be arrangedas sensor towers integrated into the side-view mirrors on the truck,farm equipment, construction equipment or the like. Sensor assemblies332 may also be positioned at different locations on the tractor unit152 or on the trailer 154, as noted above with regard to FIGS. 1C-D. Thecomputing devices 302 may communicate with the sensor assemblies locatedon both the tractor unit 152 and the trailer 154. Each assembly may haveone or more types of sensors such as those described above.

Also shown in FIG. 3A is a coupling system 334 for connectivity betweenthe tractor unit and the trailer. The coupling system 334 may includeone or more power and/or pneumatic connections (not shown), and afifth-wheel 336 at the tractor unit for connection to the kingpin at thetrailer. A communication system 338, equivalent to communication system242, is also shown as part of vehicle system 300.

Similar to FIG. 2, in this example the cargo truck or other vehicle mayalso include a user interface subsystem 339. The user interfacesubsystem 339 may be located within the cabin of the vehicle and may beused by computing devices 202 to provide information to passengerswithin the vehicle, such as a truck driver who is capable of driving thetruck in a manual driving mode.

FIG. 3B illustrates an example block diagram 340 of systems of thetrailer, such as trailer 154 of FIGS. 1C-D. As shown, the systemincludes an ECU 342 of one or more computing devices, such as computingdevices containing one or more processors 344, memory 346 and othercomponents typically present in general purpose computing devices. Thememory 346 stores information accessible by the one or more processors344, including instructions 348 and data 350 that may be executed orotherwise used by the processor(s) 344. The descriptions of theprocessors, memory, instructions and data from FIGS. 2 and 3A apply tothese elements of FIG. 3B.

The ECU 342 is configured to receive information and control signalsfrom the trailer unit. The on-board processors 344 of the ECU 342 maycommunicate with various systems of the trailer, including adeceleration system 352, signaling system 354, and a positioning system356. The ECU 342 may also be operatively coupled to a perception system358 with one or more sensors arranged in sensor assemblies 364 fordetecting objects in the trailer's environment. The ECU 342 may also beoperatively coupled with a power system 360 (for example, a batterypower supply) to provide power to local components. Some or all of thewheels/tires 362 of the trailer may be coupled to the decelerationsystem 352, and the processors 344 may be able to receive informationabout tire pressure, balance, rotation rate, wheel angle, wear, andother factors that may impact driving in an autonomous mode, and torelay that information to the processing system of the tractor unit. Thedeceleration system 352, signaling system 354, positioning system 356,perception system 358, power system 360 and wheels/tires 362 may operatein a manner such as described above with regard to FIGS. 2 and 3A.

The trailer also includes a set of landing gear 366, as well as acoupling system 368. The landing gear may provide a support structurefor the trailer when decoupled from the tractor unit. The couplingsystem 368, which may be a part of coupling system 334, providesconnectivity between the trailer and the tractor unit. Thus, thecoupling system 368 may include a connection section 370 (e.g., forcommunication, power and/or pneumatic links to the tractor unit). Thecoupling system also includes a kingpin 372 configured for connectivitywith the fifth-wheel of the tractor unit.

EXAMPLES

According to aspects of the technology, while various factors and forcescan constrain vehicle handling, a control system evaluates suchinformation and can use it to modify current driving operations or planan upcoming path or a maneuver. The factors and forces can include thefriction interaction of tires on the road surface, actuation forcesgenerated by the vehicle, and external factors. The external factors mayinclude features of the roadway, such as road grade and bank. They mayalso include environmental factors such as wind gusts, precipitation,temperature, etc.

The vehicle's available control authority is limited by several factors,which can be broadly categorized as intrinsic properties of the vehicle,and extrinsic properties associated with the external environment alongwhich the vehicle is operating. By way of example, the intrinsicproperties may include engine torque, braking torque, steering motortorques, vehicle mass, vehicle center of mass, vehicle center ofaero-pressure, etc. The intrinsic properties may typically be static orchange in discrete and well characterizable increments. For example, asteering failure associated with the vehicle's ECU may cause a stepfunction in available steering motor torque and thus available steeringrack force. And the loading of passengers into the vehicle at the outsetof a trip may cause a discrete change in the center of gravity and massof the vehicle. This change may be essentially static for the durationof the trip once passengers are seated.

The extrinsic properties of the environment may include a local gravityvector, surface friction at each wheel along the surface of the roadway,etc. The extrinsic properties can be much more dynamic and, in somecases, be much harder to predict and characterize than the intrinsicproperties. It can be helpful to further subdivide the extrinsicproperties into two categories: extrinsic forces and extrinsicmodifications. By way of example, extrinsic forces can encompass roadgrade, bank, and wind gusts, while extrinsic modifications can encompasstire force limitations due to changes in surface friction. While roadgrade (hills) and bank (on/off-ramps, etc.) are very static, predictableand can be readily identifiable using stored map information and/orinformation obtained by on-board or off-board sensors, forces such aswind pressure or reductions in surface friction due to rain, oil, snow,or ice may be very dynamic both in the spatial and temporal domains.

The forces associated with such intrinsic and extrinsic factors can beconsidered in three-dimensional space. According to one aspect of thetechnology, to maintain proper control authority of the vehicle, the sumof the intrinsic (F_(intrinsic)) and extrinsic (F_(extrinsic)) forcesprojected into the longitudinal and lateral directions relative to thevehicle should not exceed the tire force available from friction(F_(μs)) in the same direction, according to the following equation:

$\begin{matrix}{{\overset{arrow}{F_{intrinsic}} + \overset{arrow}{F_{extrinsic}}} \leq \overset{arrow}{F_{\mu_{s}}}} & ( {{Eq}.\mspace{14mu} 1} )\end{matrix}$

However, given that the magnitude of the mass of the vehicle isrelatively static during maneuvering, this equation may be reduced tofocusing on the accelerations as follows:

$\begin{matrix}{{{m\;\overset{arrow}{a_{intrinsic}}} + {m\;\overset{arrow}{a_{extrinsic}}}} \leq {m\;\overset{arrow}{a_{\mu}}}} & ( {{Eq}.\mspace{14mu} 2} ) \\{{\overset{arrow}{a_{intrinsic}} + \overset{arrow}{a_{extrinsic}}} \leq \overset{arrow}{a_{\mu}}} & ( {{Eq}.\mspace{14mu} 3} )\end{matrix}$

In other words, the system may consider the ranges of accelerations thatthe vehicle can produce and add the range of external disturbanceaccelerations. In order for control to be maintained without sliding onthe road surface, the sum of these accelerations must be less than thelimiting acceleration due to friction. This information can be used toidentify an envelope of feasible accelerations based on envelopes offriction-limited acceleration and actuator-limited acceleration, asshown in the exemplary plot 400 of FIG. 4. In particular, plot 400 showsin the dashed line 402 an envelope of friction-limited acceleration, andshows in the dash-dot line 404 an envelope of actuator-limitedacceleration. The solid line 406 represents the envelope of feasibleaccelerations in the lateral (A_(y)) and longitudinal (A_(x)) directionsrelative to the pose of the vehicle, which is constrained by theenvelopes 402 and 404.

Given this, feasible and stable acceleration may be achieved in variousvehicle/environment states if the on-board computing system (e.g.,planner module) is able to create routes, paths, short-term correctionsor other operating plans that take into account modified lateral andlongitudinal acceleration limits (and acceleration rates), which aredynamic in time and space.

One way to achieve this is via an approach that evaluates an availableacceleration model. In one example, the model may be derived from a“G-G” graphical diagram, which defines an envelope of maximumacceleration in longitudinal and lateral acceleration space (A_(x),A_(y)), which reflects the combined influence of various limitationssuch as discussed above, e.g., relating to actuator performance,friction, road bank, road grade, etc. FIG. 5 illustrates an exemplaryG-G diagram 500. As seen in this example, envelope 502 is not symmetricabout the longitudinal (Ay) axis, owing to the fact that positivelongitudinal acceleration (shown by arrow 504) in this example isactuator (e.g., propulsion) limited, whereas negative longitudinalacceleration (braking, shown by arrow 506) is friction limited. Anyimplementation of this envelope would accommodate this asymmetry.

The characteristics of the acceleration envelope may vary in severalways in response to the contributing factors described herein. Forinstance, when there is a change in friction, the entire envelope 502will shrink. In the case of an idealized circular envelope, this wouldcorrespond to a decrease in radius of the envelope. For a change in roadgrade, the entire envelope will shift vertically along the A_(x) axisdue to rotation of gravity in the vehicle frame. Here, the envelope willlikely also distort vertically as a result of longitudinal loadtransfer. For a change in road bank, the entire envelope will shifthorizontally along the A_(y) axis due to rotation of gravity in thevehicle frame. Here, the envelope will likely also distort horizontallyas a result of lateral load transfer. And for a change in actuatorcapability, this may manifest as either longitudinal or lateraldistortions in the envelope. By way of example, a change in actuatorcapability may include (a) dual wound electric motors losing one part ofthe winding, (b) reduced brake pressure built-up (rate) due to increasedfluid viscosity in low temperatures, (c) brakes limited to one hydrauliccircuit (e.g., diagonal or front/rear split) due to a hydraulic leak,(d) reduced motor performance in brakes or steering due to voltage inputdrop, (e) motors thermal derating, etc. Therefore, the implementation ofthe envelope according to aspects of the technology supports shifting,scaling, and distortion as needed.

In order to avoid a loss of traction event, according to one aspect thetrajectory analysis accounts for the available friction and limitsforces/accelerations to be less than the available friction force. Thisincludes evaluating both the tire state and the friction between thetires and the road surface.

The state of the tires can be estimated to understand how the tires willinteract with the driving surface in order to create the frictionenvelope. Tire state estimation is used to capture one or more of thetire slip angle, tire longitudinal and/or lateral slip, tire normalforce, the contact patch size and location, the tire deformation, tirematerial temperature, and any other parameter intrinsic to the vehicle'stire that would change the ability of the tire to stick to the roadsurface. According to one aspect of the technology, tire estimation maybe performed per tire (including, e.g., longitudinal and lateral slip,etc.). There may be one friction coefficient estimate for all tires, butthere can be situations identified as mu split (different left rightbraking surfaces). Tire temperature could be evaluated generally on thevehicle level, but could also be evaluated on a per-tire basis. Forlarge vehicles such as cargo trucks, there may be 2 or more steeringtires, 8 or more drive tires for the tractor, and 8 or more trailertires. These different sets of tires could be evaluated as separategroups or on an individual basis. Note that the amount of tire wear caninfluence both force build-up as-well-as effective rolling radius (whichis relevant to the longitudinal slip estimation).

The properties of tire-road surface interaction are estimated to modelthe force limits of the vehicle's tires, e.g., using a parametric modelof the tires. This factor captures the extrinsic property of the drivingsurface that determines (when combined with the tire's state) theenvelope of available friction. By way of example, the driving surfacemay be asphalt, concrete, gravel, paving stone, brick or other type ofpavement. The driving surface may change depending on whether the roadsegment is a surface street, highway, bridge, etc. It may also changedue to construction, such as when a steel plate covers a stretch ofroadway or asphalt is used to patch areas of a concrete surface.Estimation of tire-road surface interaction could be as complex as anon-line friction estimation or as simple as a parameter adjusted byoffboard weather monitoring. A lookup table could be used for differentroad surfaces and/or weather conditions. Offline characterized tireparameters can be used for different friction coefficients. Byestimating the tire's lateral and longitudinal forces and theirestimated tire slip state, one could back estimate the frictioncoefficient of the tire. Alternatively or additionally, online frictionestimation methodologies may also be employed. This can includeestimation by tire force and slip angle estimation and fitting a tirecurve online, estimation by detecting a reduction in pneumatic trail viasteering torque measurements, and/or acoustic methodologies that useaccelerometers embedded in the tires.

As noted above, according to another aspect of the technology thetrajectory analysis also evaluates external forces on the vehicle. Theexternal forces on the vehicle are estimated because they willcontribute to the total force on the vehicle, which needs to stay belowa friction threshold in order for traction to be maintained on theroadway. This evaluation can include both local gravity vectorestimation and random or variable external force estimation(environmental force estimation).

The local gravity vector estimate is a measure of the local bank andgrade of the roadway, which affects the total available acceleration.The local gravity vector will also cause body pitch, body roll, loadtransfer between tires, and torque moments depending on orientation withrespect to the vehicle heading. Detailed maps may be used that containinformation for road grade and banking. Fusing this information with astate estimator (such as a Kalman filter) that utilizes inertialmeasurement sensors (e.g., accelerometers and gyroscopes) together withspeed information such as from a Global Navigation Satellite System(e.g., GPA) and the wheel speed sensing can be employed to identifywhich part of the acceleration is due to road grade and/or banking, andwhich due to vehicle motion control.

The environmental or random/variable external force estimation capturesa sense of the expected random disturbance forces (e.g., wind, roughroad surfaces). Initially this is likely implicitly assumed to belimited by the operational design domain; however, for scaled deploymentwith optimal motion control performance, external disturbances could bemodelled and taken into account (e.g., using a wind gauge to estimatethe side forces on trailer due to wind). The operational design domainmay encompass the area(s) in which vehicles are deployed (e.g., whichpart of a city), the time of day (or season), the traffic conditions,the weather conditions, etc. By way of example, driving at 6:00 pm in acity such as San Francisco or New York City in the middle of a snowywinter may be more challenging than driving at 2:00 am during thesummertime in Miami or Phoenix. A sense of mean and variance in randomexternal forces could be used to either inform maneuvers that are likelyto be executed with little error, or the estimation information could bepassed to the planner module to inform lateral gap evaluation withregard to object planning, such as how close the vehicle can drive withregard to a parked car or other roadway object. By way of example, ifdata indicates that there are disturbances that will cause poor positioncontrol performance (e.g., beyond some threshold value), then accordingto one aspect the planner would keep greater gaps to objects due to theuncertainty of the position error that can be achieved. Statistically,this can be understood by the mean and standard deviation of theposition error as a function of various conditions. Thus, in one drycondition scenario the planner could always be controlling the vehicle'slateral position within 10 cm for 99.999% of the time. Under theassumption that there always will be an agent-object adjacent to thevehicle, if a minimum lateral gap of 10 cm is maintained, then thelikelihood of a collision would be 0.001%. Another option is Monte Carlosimulation of disturbances (e.g., with some assumption on what thedistribution of disturbances should look like) using a dynamic model ofsufficient fidelity to set planner lateral gaps under differentconditions.

A further aspect of the technology estimates the internal forcecapability on the vehicle. In particular, the available internal forcegenerating capability of the vehicle should be understood in order toensure that the vehicle is capable of achieving the desiredaccelerations, even if they are allowed by the extrinsic factors. Thiscan include one or more of the following estimations: steering systemstate, braking system state, propulsion system state and vehicleproperties state.

The steering system state estimation can be used to capture anyinformation that affects the ability of the steering subsystem to applyforce/acceleration to the vehicle. This can include information such asrack motor power limitations, rack inertia, the number of activeelectronic control units or other control modules, motor torque responsefunctions, control mode, internal limiters, etc. Braking system stateestimation may capture any information that affects the ability of thebraking subsystem to apply force/acceleration to the vehicle. This caninclude information such as pump motor power limitations, stabilityintervention events, the number of active electronic control units orother control modules, hydraulic pressure state, the amount ofregenerative braking available, control mode, internal limiters, etc.Propulsion system state estimation may capture any information thataffects the ability of the powertrain subsystem to applyforce/acceleration to the vehicle. This can include information such asmotor power limitations, motor torque response functions, hystereticeffects, fault condition, control mode, internal limiters, etc. Andvehicle (kinetic) properties state estimation may capture informationsuch as the mass properties of the vehicle and encode the current stateof motion. Fluid level reservoirs, current sensors, encoders to measureposition and estimate speed and acceleration may all be employed. Manyabnormalities can be diagnosed using models. For instance, for aspecific displacement of a hydraulic piston, there would be anexpectation for a certain amount of pressure to build up. If thepressure is not building up with the expected rate, this would beindicative of a leak.

FIG. 6 illustrates a functional architecture 600 that evaluates theintrinsic and extrinsic information described above to generate anavailable acceleration model. The estimations and evaluations may bedone by the on-board processing system (e.g., 202 of FIG. 2 or 302 ofFIG. 3A), for instance using various estimation modules. In particular,tire state estimation is performed at block 602 and surface coefficientof friction estimation is performed at block 604. Local gravity vectorestimation (in accordance with forces associated with road banking andgrade) is performed at block 606 while environmental forces estimation(e.g., random/variable external force estimation due to wind disturbanceor rumble) is performed at block 608. Note that these factors wouldchange the shape of the envelope for friction-limited acceleration(dashed line 402 in FIG. 4). For instance, going uphill, the wholeellipse in plot 400 of FIG. 4 would shift toward the bottom. Steeringsystem state estimation is performed at block 610, braking system stateestimation is performed at block 612, propulsion system state estimationis performed at block 614 and vehicle kinetic properties stateestimation is performed at block 616. While such estimations are shownas being performed in discrete blocks, they may also be donecollectively via one or more modules. In one scenario, if the propulsionfrom the acceleration system can only deliver 3 m/s² longitudinalacceleration, that sets a cap to the vehicle's acceleration. If thebrakes of the deceleration system can deliver up to −10 m/s² then thatwould set a threshold for longitudinal acceleration (deceleration). Andif the steering system can only steer up to 5 m/s² due to a systemsoftware limitation or a fault, then that would set a limit on thelateral acceleration. Thus, how different actuators (e.g., accelerationsystem, deceleration system, steering system) operate have an impact onthe overall vehicle performance. It is also useful to consider the ratesthat the actuators can develop the forces, shown in a steady-stateexample in the g-g diagram. For efficient planning, the planner moduleshould also be aware of the rate that the vehicle can move within theg-g diagram.

As shown in this architecture, information from the tire stateestimation block 602 and the surface coefficient of friction estimationblock 604 are analyzed in local friction envelope estimate block 618.For instance, the local friction envelope estimate module consumesinformation from blocks 602 to 604 to decide how the performance limitsdue to friction should be adjusted. This corresponds to a scaling of theg-g diagram for the vehicle in g-g diagram 500. By way of example, usingthe tire state estimation, longitudinal and lateral slip and an adaptivevalue for the friction coefficient, the vehicle level friction envelopecan be derived. Here, the system may also consider scenarios in whichthe wheels have different friction coefficients (e.g., split muscenarios). The information from the local gravity vector estimationblock 606 and the environmental forces estimation block 608 are analyzedat the external force on vehicle estimate block 620. In particular, thisblock consumes information from the local gravity vector estimation andthe environmental forces estimation in order to decide how theperformance limits due to external forces should be adjusted. The firstorder effect of this is a shifting of the g-g diagram for the vehicle(though there may be some distortion as a second order effect). And theintrinsic vehicle-related information from blocks 610-616 are evaluatedby internal force on vehicle estimate block 622. This block consumesinformation from its inputs to decide how performance limits due toactuator limitations should be adjusted. For example, if the brake forceactuation should become limited (e.g., due to a hydraulic leak), thenthe bottom of the g-g diagram will be distorted (the lower extreme willmove upward). The influence of external disturbances can have anoticeable influence on the estimate. Thus, according to one aspect thesystem should have knowledge on the magnitude of the disturbances to seehow the g-g plot may be affected. For instance, this could be doneconservatively, e.g., by identifying that the maximum state accelerationdisturbance due to wind or potholes is 1 m/s² and reduce the overallsize of the g-g diagram accordingly.

The results from the estimations at blocks 618, 620 and 622 areincorporated together at block 624 to generate an available accelerationmodel. Based on this, the on-board planner module or other portion ofthe processing system can produce a traction generation profile (e.g., avariable motion control envelope) at block 626. This profile can beupdated continuously, periodically (e.g., every 0.1-2.0 seconds, or moreor less), between iterations of the path generated by the planner, orupon the occurrence of an action, event or other condition that mayimpact the motion control envelope. In addition to being updatedtemporally, the profile can also be updated spatially. For instance, ifa portion of the planned trajectory is on a dry road segment and aportion is on a wet road segment, trajectory waypoints on the wetsection could have a reduced friction coefficient and consequently ashrunken g-g diagram. The output from block 626 can then be used by thecontrol system of the vehicle at block 628 to change driving actions orupdate an operating plan for an upcoming portion of the trip along aselected portion of the roadway. This could include modifying a brakingor accelerating operation, altering the planned path of the vehicle, ortaking another course of action.

FIGS. 7A-B illustrate an example architecture 700 that implements aselected subset of the functional architecture discussed above in orderto produce a traction generation profile and use that information forvehicle control in an autonomous driving mode. In the examplearchitecture 700, surface friction estimation acts as a primary input toan available acceleration model, in particular an acceleration envelopemodel. The acceleration envelope model then provides dynamically varyingacceleration limits, e.g., to a planner module of the processing system,which uses this information to generate a trajectory used whencontrolling the vehicle.

In this example, road service classification information 702 and weatherdata 704 are inputs to a proactive friction estimation block 706. Outputfrom block 706 is an initial friction estimate 708. For instance, if thesystem knows that it is raining or snowing in an area based on weatherdata 704, it can set the friction bounds accordingly to be lower, e.g.,for a dry road surface the friction bounds may be between [0.9 to 1],while for a wet road surface it may be on the order of [0.6 to 0.9] andfor snow from [0.2 to 0.4] depending on the tires. In addition, the roadsurface classification (702) may be weighted more heavily than theweather data (704), as the road surface classification would representthe most localized indication that impacts the proactive frictionestimation (706). For instance, the weighting may be in ratios of, e.g.,60:40, 70:30 or 80:20 (or more or less) based on the type ofclassification and/or the type of precipitation.

The initial friction estimate 708 and other information, in particularvehicle pose 710 and wheel speeds 712, are input into block 714 foradaptive friction estimation. The wheel speeds 712 may be a subset ofthe tire state estimation information from block 602 of FIG. 6. In onescenario, there may be additional inputs 715 to the adaptive frictionestimation 714, such as actuation forces and tire normal forceestimation. This information may indicate how much braking/propulsiontorque the vehicle is putting into the tires. For instance, it can behelpful to know what is “asked” from the tires vs what the tires deliverto be able to estimate their potentials. The normal load is fundamentalto understand how much vertical force is exerted.

The adaptive friction estimation block 714 utilizes this inputinformation to generate an on-line friction estimate 716 duringreal-time driving.

Block 718 uses both the vehicle pose 710 and the on-line frictionestimate 716 in an acceleration envelope model, such as availableacceleration model 624 of FIG. 6. The output of block 718 is a set ofacceleration limits 720, which effectively scales the g-g diagram inresponse to changes in friction. Thus, block 718 can conceptually beviewed as encompassing the functional architecture 600 prior to controlof the vehicle.

As shown in FIG. 7B, the on-line friction estimate 716 and the vehiclepose 710 information are input into limit recovery control block 722,which generates recovery state information 724. According to onescenario, limit recovery control 722 is tasked with augmenting theinputs generated by path tracking control of the control block (e.g.,block 628 in FIG. 6) if the vehicle is approaching or has reached thefriction limits. This can occur when the tire-road friction coefficientis lower than predicted, such as might happen if the vehicle travelsover a patch of reflective paint on a wet roadway. The purpose of theseaugmented inputs will be to direct the vehicle state back to a regimethat is away from the handling limits. However, in some situations itmay be the case that the limit recovery objective conflicts with thepath tracking objective. Here, it may be necessary to temporarily inducelarger positional errors for the sake of maintaining stable vehiclebehavior by avoiding the handling limits. For this reason, limitrecovery control block 722 would provide status in the form of recoverystate information 724 (e.g., NOT_ACTIVE, ACTIVE) to the motion plannerblock 726 (e.g., of the planner module) for the purpose of adaptingplanner behavior in this scenario.

Another way to approach this is to imagine that a path is being tracked.Due to a limit handling situation such as hitting a patch of ice, thevehicle will deviate from its intended path. The limit recoverycontroller 722 can momentarily disregard the path being tracked and willtry to get the vehicle stable, which could be done by understeering. Therecovery control could try to reduce the speed to and potentiallydecrease the steering angle to go back into a stable trajectory, whichcould be fed back to the planner. Thus, the recovery state can be viewedas a target trajectory that will stabilize the vehicle. The planner canthen accordingly replan from the current vehicle state and the same timecould decrease the vehicle motion envelope (see FIG. 4) due touncertainty of the traction limits Therefore, in one example, for block722 the inputs would include vehicle pose, the on-line frictionestimate, as-well-as the actual trajectory of the vehicle.

The limit recovery control block 722 can also be viewed assimultaneously providing inputs to bring the vehicle back within acertain state envelope (via corrective control inputs 734) while alsofeeding back an indication that traction loss has occurred (recoverystate 724), either through a binary flag or updated/reduced limits. Thedistinction here is that limit recovery control is not responsible forgenerating/proposing a new trajectory, but maintaining vehicle stabilitywhile signaling that a change in planned trajectory is required. Thus,in this scenario the actual trajectory would not be necessary as aninput to block 722.

The set of acceleration limits 720 and the recovery state information724 are input to motion planner block 726, and a trajectory 728 isoutput to path tracking control block 730 of the control section. In oneexample, inputs to the motion planner 726 (the acceleration limits 720)correspond to the acceleration information from FIG. 5, e.g., theactuator rate limits (in other words the speed the vehicle can movewithin the trace of the G-G diagram), a route (e.g., where the vehicleis driving), and a set of path constraints (e.g., what is the pathocclusion due to obstacles). Thus, in this situation, the primarycontrol inputs would be feedforward (e.g., how much torque is needed tomaintain steady state speed over this grade, what are the vehicle'saerodynamic losses, what is the vehicle's rolling resistance, etc.) andfeedback commands (e.g., how much path tracking error is there) of apath tracking controller. As shown, path tracking control block 730 alsoreceives the on-line friction estimate 716. In one scenario, the pathtracking control 730 additionally receives instantaneous accelerationslimits. Here, for instance, if the vehicle is on a grade or a road bank,that information can help to generate the correct feedforward commandfor the path tracking control 730.

Output from the path tracking control block 730 is a set of primarycontrol inputs 732. A set of corrective control inputs 734 is output bythe limit recovery control block 722 (in addition to the recovery stateinformation 724). The primary and corrective control inputs are mixedtogether at 736, with a resultant set of net control inputs 738 beingthe result. The net control inputs 738 are then used by the processingsystem to control operation of the vehicle in the autonomous drivingmode.

Note that the components of the example architecture may becharacterized as being either proactive, adaptive, or reactive incharacter. For instance, proactive components output an anticipatedfriction coefficient (e.g., initial friction estimate 708 from block706) based on prior/offboard analysis of multiple sources of contextualinformation such as the road surface classification 702 and weather data704. Adaptive components such as block 714 refine the vehicle's currentnotion of friction based upon real-time estimation techniques thatestimate the true friction coefficient prior to the vehicle encounteringthe friction limits, for instance by using the vehicle's poseinformation 710 and wheel speeds 712 in conjunction with the initialfriction estimate 708. Reactive components such as limit recoverycontrol block 722 respond to a degradation in motion control performancewhen the vehicle unexpectedly encounters its friction limits. Thesecomponents are tasked with both maintaining acceptable (but temporarilyrelaxed) position error bounds and providing feedback to the plannermodule as needed.

A robust implementation of a variable motion control envelope mayinclude all three component types, through proactive frictionestimation. For instance, in one scenario proactive friction estimationutilizes a combination of perception and weather data to estimate theextent and severity of road wetness, which is in turn used to predictthe road-tire friction coefficient in a data-driven fashion based onprior analysis. Adaptive friction estimation utilizes motion sensing,models of the tires and vehicle dynamics in on-line real-time estimationto estimate a tire-road friction coefficient. A guiding principle ofthese estimation techniques is that it is possible to estimate tire-roadfriction at the onset of nonlinearity in the tire's force-slip curve,but prior to the tire reaching its friction limits.

Friction estimation using such wheel slip-based techniques require thevehicle to brake at a high enough magnitude to provide sufficientexcitation for observer convergence. For instance, in order to estimatenon-linear effects, the system needs to operate temporarily in thenon-linear region

As discussed herein, the acceleration envelope model according toaspects of the technology takes a current best estimate of friction anduses it to adapt the envelope for a given vehicle platform.Identification of the envelope as well as its variation with frictioncan be conducted through offboard, model-driven analysis. This analysiseffectively amounts to identifying the acceleration limits up to whichthe model remains both stable and controllable as the modeled tire-roadfriction is varied. In one example, implementation of this model wouldbe lookup-table based, with the lookup tables generated based uponoffboard, model-driven analysis to identify the vehicle handling limits.

Several approaches could be employed, including virtual kinematicallyconstrained testing, race line optimization in simulation, and empiricalidentification by a skilled driver on a closed circuit. With regard tothe first approach, the Milliken Moment Method (MMM) may be employed. Bygenerating MMM “runs” across a range of longitudinal inputs, it is thenpossible to generate a G-G diagram for a given road bank and grade. Itis then possible to explore a range of values for road bank and gradeand generate a G-G diagram for each road geometry. While this approachcould be implemented using a fairly simple model to generate a proof ofconcept, a more robust approach would be when this approach isimplemented with a higher fidelity model that incorporates asemi-empirical tire model and a suspension model with associated lateraland longitudinal load transfer effects.

According to one aspect of the technology, the control componentdesirably includes both adaptive and reactive sub-components. Theadaptive and reactive sub-components have objectives of path trackingand maintaining vehicle stability, respectively. According to anotheraspect, the system may employ model predictive control.

In another scenario, path tracking control is desirably adaptive in thesense that the feedforward path is able to adapt as the on-line frictionestimate changes. For instance, consider the steady-state handlingcharacteristics of an exemplary self-driving vehicle as obtained on drypavement. In this example, below about 4 m/s² of lateral acceleration,there may be an approximately linear relationship between lateralacceleration and steer angle. Above about 4 m/s′, the relationshipbecomes nonlinear as the front tires become friction-limited (known aslimit understeer). The onset of nonlinearity in this characteristic isfriction-dependent, so effective feedforward control will vary with theon-line friction estimate. There is also a possibility that a feedbackpath would need to be adaptive as well, with a technique such asgain-scheduling used to adapt to changes in the on-line frictionestimate.

As noted above, the technology is applicable for various types ofself-driving vehicles, including passenger cars, buses, motorcycles,emergency vehicles, RVs, construction vehicles, and large trucks orother cargo carrying vehicles. In addition to using the variousintrinsic and extrinsic information for operation of an individualself-driving vehicle, relevant information may also be shared with otherself-driving vehicles, such as vehicles that are part of a fleet. Suchinformation may include information relating to road surfaces, weatherdata, etc.

One example of a fleet approach is shown in FIGS. 8A and 8B. Inparticular, FIGS. 8A and 8B are pictorial and functional diagrams,respectively, of an example system 800 that includes a plurality ofcomputing devices 802, 804, 806, 808 and a storage system 810 connectedvia a network 816. System 800 also includes vehicles 812 and 814configured to operate in an autonomous driving mode, which may beconfigured the same as or similarly to vehicles 100 and 150 of FIGS.1A-B and 1C-D, respectively. Vehicles 812 and/or vehicles 814 may bepart of a fleet of vehicles. Although only a few vehicles and computingdevices are depicted for simplicity, a typical system may includesignificantly more.

As shown in FIG. 8B, each of computing devices 802, 804, 806 and 808 mayinclude one or more processors, memory, data and instructions. Suchprocessors, memories, data and instructions may be configured similarlyto the ones described above with regard to FIG. 2 or 3A.

The various computing devices and vehicles may communication directly orindirectly via one or more networks, such as network 816. The network816, and intervening nodes, may include various configurations andprotocols including short range communication protocols such asBluetooth™, Bluetooth LE™, the Internet, World Wide Web, intranets,virtual private networks, wide area networks, local networks, privatenetworks using communication protocols proprietary to one or morecompanies, Ethernet, WiFi and HTTP, and various combinations of theforegoing. Such communication may be facilitated by any device capableof transmitting data to and from other computing devices, such as modemsand wireless interfaces.

In one example, computing device 802 may include one or more servercomputing devices having a plurality of computing devices, e.g., a loadbalanced server farm, that exchange information with different nodes ofa network for the purpose of receiving, processing and transmitting thedata to and from other computing devices. For instance, computing device802 may include one or more server computing devices that are capable ofcommunicating with the computing devices of vehicles 812 and/or 814, aswell as computing devices 804, 806 and 808 via the network 816. Forexample, vehicles 812 and/or 814 may be a part of a fleet ofself-driving vehicles that can be dispatched by a server computingdevice to various locations. In this regard, the computing device 802may function as a dispatching server computing system which can be usedto dispatch vehicles to different locations in order to pick up and dropoff passengers or to pick up and deliver cargo. In addition, servercomputing device 802 may use network 816 to transmit and presentinformation to a user of one of the other computing devices or apassenger of a vehicle. In this regard, computing devices 804, 806 and808 may be considered client computing devices.

As shown in FIG. 8A each client computing device 804, 806 and 808 may bea personal computing device intended for use by a respective user 818,and have all of the components normally used in connection with apersonal computing device including a one or more processors (e.g., acentral processing unit (CPU)), memory (e.g., RAM and internal harddrives) storing data and instructions, a display (e.g., a monitor havinga screen, a touch-screen, a projector, a television, or other devicesuch as a smart watch display that is operable to display information),and user input devices (e.g., a mouse, keyboard, touchscreen ormicrophone). The client computing devices may also include a camera forrecording video streams, speakers, a network interface device, and allof the components used for connecting these elements to one another.

Although the client computing devices may each comprise a full-sizedpersonal computing device, they may alternatively comprise mobilecomputing devices capable of wirelessly exchanging data with a serverover a network such as the Internet. By way of example only, clientcomputing devices 806 and 808 may be mobile phones or devices such as awireless-enabled PDA, a tablet PC, a wearable computing device (e.g., asmartwatch), or a netbook that is capable of obtaining information viathe Internet or other networks.

In some examples, client computing device 804 may be a remote assistanceworkstation used by an administrator or operator to communicate withdrivers of dispatched vehicles. Although only a single remote assistanceworkstation 804 is shown in FIGS. 8A-B, any number of such workstationsmay be included in a given system. Moreover, although operationsworkstation is depicted as a desktop-type computer, operationsworkstations may include various types of personal computing devicessuch as laptops, netbooks, tablet computers, etc. By way of example, theremote assistance workstation may be used by a technician or other userto help evaluate extrinsic information such as road surface type, roadgrade, road banking, or wind gusts and their impact on estimating thelocal friction envelope. It may also be used to classify suchinformation, and/or identify appropriate responses (e.g., an availableacceleration model, traction generation or other operating plan) by theself-driving vehicle. The result of this evaluation may be provided toone or more other vehicles traveling along the same section of roadway.Additionally, this also might be the process used for obtaining labeleddata to: 1) evaluate the accuracy of this approach; and 2) train anynets involved.

Storage system 810 can be of any type of computerized storage capable ofstoring information accessible by the server computing devices 802, suchas a hard-drive, memory card, ROM, RAM, DVD, CD-ROM, flash drive and/ortape drive. In addition, storage system 810 may include a distributedstorage system where data is stored on a plurality of different storagedevices which may be physically located at the same or differentgeographic locations. Storage system 810 may be connected to thecomputing devices via the network 816 as shown in FIGS. 8A-B, and/or maybe directly connected to or incorporated into any of the computingdevices.

Storage system 810 may store various types of information. For instance,the storage system 810 may store autonomous vehicle control softwarewhich is to be used by vehicles, such as vehicles 812 or 814, to operatesuch vehicles in an autonomous driving mode. Storage system 810 may alsostore driver-specific or nominal driving models, as well as models ofthe tires and vehicle dynamics. The model information may be shared withspecific vehicles or the fleet as needed. It may be updated in realtime, periodically, or off-line as additional driving information isobtained. The storage system 810 can also include detailed mapinformation, route information, weather information, etc. Thisinformation may be shared with the vehicles 812 and 814, for instance tohelp with real-time driving or route planning by a particular vehicle.

FIG. 9 illustrates an example method of operation 900 in accordance withthe above discussions for operating a vehicle in an autonomous drivingmode. As shown in block 902, the method includes estimating, by one ormore processors of the vehicle, a local friction envelope based on atleast one of road surface information and tire state data from one ormore tires of the vehicle. At block 904, an external force impact on thevehicle is estimated based on at least one of a local gravity vector andenvironmental forces. At block 906, an internal force impact on thevehicle is estimated based on at least one of steering, braking,propulsion or vehicle kinetic information of the vehicle. At block 908,the system generates an available acceleration model for the vehiclebased on the estimated local friction envelope, the estimated externalforce impact and the estimated internal force impact. At block 910, atraction generation profile is produced based on the availableacceleration model. And at block 912 the vehicle is controlled in theautonomous driving mode according to the traction generation profile.

FIG. 10 illustrates an example method of operation 1000 in accordancewith the above discussions for operating a vehicle in an autonomousdriving mode. This includes, as shown in block 1002, generating aninitial friction estimation based on a road surface classification for aportion of a roadway and weather data for an external environment of thevehicle. Generating, per block 1004, an on-line friction estimate basedon the initial friction estimation, pose information of the vehicle onthe portion of the roadway, and wheel speed information of the vehicle.Generating, per block 1006, a set of acceleration limits based on theon-line friction estimate and the pose information. And controlling thevehicle along the roadway in the autonomous driving mode according tothe set of acceleration limits, as shown in block 1008.

Although the technology herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent technology. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present technology as defined by the appended claims.

1. A method of operating a vehicle in an autonomous driving mode, themethod comprising: estimating, by one or more processors of the vehicle,a local friction envelope based on at least one of road surfaceinformation and tire state data from one or more tires of the vehicle;estimating, by the one or more processors, an external force impact onthe vehicle based on at least one of a local gravity vector andenvironmental forces; estimating, by the one or more processors, aninternal force impact on the vehicle based on at least one of steering,braking, propulsion or vehicle kinetic information of the vehicle;generating, by the one or more processors, an available accelerationmodel for the vehicle based on the estimated local friction envelope,the estimated external force impact and the estimated internal forceimpact; producing, by the one or more processors, a traction generationprofile based on the available acceleration model; and controlling thevehicle, by the one or more processors in the autonomous driving mode,according to the traction generation profile.
 2. The method of claim 1,wherein controlling the vehicle includes at least one of changing adriving action or updating an operating plan for an upcoming section ofroadway.
 3. The method of claim 1, wherein the traction generationprofile comprises a variable motion control envelope that is updatedperiodically during operation in the autonomous driving mode.
 4. Themethod of claim 1, wherein the traction generation profile comprises avariable motion control envelope that is updated between iterations of apath generated by the one or more processors.
 5. The method of claim 1,wherein the traction generation profile comprises a variable motioncontrol envelope that is updated upon occurrence of an action, event orcondition impacting the motion control envelope.
 6. The method of claim1, further comprising updating the traction generation profile spatiallyaccording to different segments of a roadway.
 7. The method of claim 1,wherein estimating the local friction envelope is based on the tirestate data, longitudinal and lateral slip information, and an adaptivevalue for a friction coefficient of the road surface information.
 8. Themethod of claim 1, wherein the local gravity vector is a measure of alocal bank and a grade of a roadway segment.
 9. The method of claim 1,wherein the environmental forces include wind disturbance information.10. A vehicle configured to operate in an autonomous driving mode, thevehicle comprising: a perception system including one or more sensors,the one or more sensors being configured to receive sensor dataassociated with an external environment of the vehicle including aportion of a roadway; a driving system including a steering subsystem,an acceleration subsystem and a deceleration subsystem to controldriving of the vehicle; a positioning system configured to determine acurrent position of the vehicle; and a control system including one ormore processors, the control system operatively coupled to the drivingsystem, the perception system and the positioning system, the controlsystem being configured to: estimate a local friction envelope based onat least one of road surface information and tire state data from one ormore tires of the vehicle; estimate an external force impact on thevehicle based on at least one of a local gravity vector along theportion of the roadway and environmental forces in the externalenvironment; estimate an internal force impact on the vehicle based onat least one of steering, braking, propulsion or vehicle kineticinformation of the vehicle; generate an available acceleration model forthe vehicle based on the estimated local friction envelope, theestimated external force impact and the estimated internal force impact;produce a traction generation profile based on the availableacceleration model; and control the vehicle in the autonomous drivingmode according to the traction generation profile.
 11. A method ofoperating a vehicle in an autonomous driving mode, the methodcomprising: generating, by one or more processors of the vehicle, aninitial friction estimation based on a road surface classification for aportion of a roadway and weather data for an external environment of thevehicle; generating, by the one or more processors, an on-line frictionestimate based on the initial friction estimation, pose information ofthe vehicle on the portion of the roadway, and wheel speed informationof the vehicle; generating, by the one or more processors, a set ofacceleration limits based on the on-line friction estimate and the poseinformation; and controlling the vehicle along the roadway, by the oneor more processors in the autonomous driving mode, according to the setof acceleration limits.
 12. The method of claim 11, wherein generatingthe initial friction estimate includes adjusting friction boundsaccording to a wetness along the portion of the roadway.
 13. The methodof claim 11, wherein generating the initial friction estimate includesweighting the road surface classification more heavily than the weatherdata.
 14. The method of claim 11, wherein the on-line friction estimateis further based on additional information associated with how muchtorque is applied to one or more tires of the vehicle.
 15. The method ofclaim 14, wherein the additional information includes at least one ofactuation forces or a tire normal force estimation.
 16. The method ofclaim 11, wherein the on-line friction estimate is adaptive in real-timeduring driving along the portion of the roadway in accordance with thepose information and wheel speed information.
 17. The method of claim11, wherein generating the set of acceleration limits includesgenerating a set of corrective control inputs and recovery stateinformation.
 18. The method of claim 17, wherein the recovery stateinformation provides a target trajectory for stabilizing the vehicle.19. The method of claim 11, wherein the set of acceleration limits isassociated with a set of corrective control inputs and a set of primarycontrol inputs, the set of corrective control inputs being obtained fromthe on-line friction estimate and the pose information, and the set ofprimary control inputs being obtained from the on-line friction estimateand trajectory information of the vehicle.
 20. The method of claim 19,wherein controlling the vehicle is performed based on a combination ofthe corrective control inputs and the primary control inputs.